Bill McKibben laid out a clear climate agenda for the Vermont Legislature on Wednesday when he appeared as the guest of House Speaker Shap Smith to speak in the House chamber for legislators and the public.

McKibben, who lives in Ripton and teaches at Middlebury College, is one of the nation’s leading climate activists and a pioneering author on climate change. He led a massive exercise of civil disobedience at the White House last summer in opposition to the Keystone XL pipeline and continues to promote the activities of 350.org, an international effort to raise awareness of climate change.

At the end of McKibben’s talk, a legislator asked him what his priorities would be for legislative action. McKibben did not hesitate. First, he said, pass legislation to improve thermal efficiency for Vermont buildings. Second, block the flow of tar sands oil through a pipeline in northern Vermont. Third, get rid of holdings by state pension funds and the University of Vermont endowment in fossil fuel companies.

McKibben’s presentation was clear and fact-based. His proposals may seem radical, except in the context of the radical threat that mankind faces. In that context, McKibben and his ideas are the model of reason.

He outlined the situation as it exists. He said last summer that the polar ice cap was half the size it was when Neil Armstrong looked down on it in 1969. He referred to the vast melting as “catastrophic.”

He said the oceans are 30 percent more acidic than they were 40 years ago, with unknown consequences for the marine life upon which humans and the broader ecosystem depend.

He said the atmosphere now contains 5 percent more moisture than 40 years ago. We have seen the results in the form of disastrous storms and floods. He said Tropical Storm Irene was a “defining event” for Vermont. The state saw the greatest rainfall in its history: 11.23 inches in Mendon.

The trajectory of climate change is leading toward more extreme conditions. Humans have raised the temperature of the atmosphere by 1 degree and have burned sufficient fossil fuel already so that in time we can expect the temperature will rise by another degree. He called that 2 degree rise a “red line.” Temperatures beyond that line take us into territory with incalculable consequences.

He said the World Bank had already predicted that temperatures could rise by 4 to 6 degrees. The only way to avoid a catastrophic outcome is to leave in the ground 80 percent of the known oil, gas and coal reserves, a proposition that oil and coal companies will not willingly embrace.

It is to slow or discourage the extraction of tar sands oil in Alberta that McKibben believes Vermont should take a hand in by blocking the pipeline that would take tar sands oil from Montreal to the port of Portland, Maine.

McKibben opposes a moratorium on ridgeline wind power, noting it would be supremely ironic if the U.S. House had passed wind energy credits in January only to see the Vermont House reject wind development.

Electricity generated from sustainable sources is our main hope. It could power our cars and fuel our industries. He said neither wind nor solar power was a “silver bullet.” What we need, instead, is “silver buckshot,” promoting alternatives on all fronts. We must be wise about where we site our wind turbines, but we cannot say no now.

He said Seattle had already divested itself of its fossil fuel holdings; the mayor there had said it made no sense to spend millions of dollars building sea walls but investing in companies that make the sea walls necessary.

McKibben left the legislators with an urgent piece of advice: “Just as we must adapt to that which we can’t prevent, we must prevent that to which we can’t adapt.”

It will be hard to adapt to a world in which Irene is the norm. But that is where we are headed. All signs point to it, and we are heading there faster than scientists had expected. McKibben described some simple steps for preventing the worst, and the Legislature ought to pay attention.